1. Field of the Invention
This invention relates to aerosols of antiallergic drugs and, more particularly, to suspension type aerosol inhalations containing pyrido[1,2 -a]pyrimidine compounds of the formula: ##STR2## where R is a n-propyl or allyl group, A is a tetrazolyl or carboxyl group, and n is a whole number of 0 to 2.
2. Description of the Prior Art
Pyrido[1,2-a]pyrimidine compounds represented by the above formula are the compounds disclosed in Japanese Patent Laid-Open Nos. 242682/'87, 183581/'88 and 246375/'88. It is described therein that these compounds have a powerful inhibitory effect on leukotrien D4 known to be a representative active component of slow-reacting substance of anaphylaxis (hereinafter referred to as SRS-A) and, therefore, are useful as drugs for the treatment of Type I allergic diseases induced by SRS-A.
At present, commercially available antiallergic agents are principally in the form of oral preparations. However, oral preparations are not always regarded as a proper dosage form, because they generally involve an increase in dose and hence lead to the manifestation of side effects. Especially for bronchial asthma and allergic rhinitis, topical preparations for applying a drug directly to the affected part, particularly inhalations, are considered to be an effective dosage form in that they can produce drug effects efficiently and mitigate side effects.
Inhalations for use as antiallergic agents included aqueous solution type aerosol inhalations, solution type aerosol inhalations and suspension type aerosol inhalations. The solubilities of pyrido[1,2-a]pyrimidine compounds in water are very low. For example, the solubility of 9-[(4-acetyl-3-hydroxy-2-n-propylphenoxy)methyl]-3-(1H-tetrazol-5-yl)-4-H- pyrido[1,2-a]pyrimidin-4-one (hereinafter referred to as AS-35) in water is as low as 0.4 ,.mu.g/ml. Accordingly, it would be impractical to prepare an aqueous solution type aerosol inhalation of AS-35, because this requires massive containers and devices. Moreover, in order to prepare a solution type aerosol inhalation of a pyrido[1,2-a]pyrimidine compound, it must be dissolved in a propellant or a mixture of a propellant and a commonly used solubilizing agent. However, AS-35 is entirely insoluble in commonly used propellants including trichloromonofluoromethane (Freon 11), dichlorodifluoromethane (Freon 12), monochlorotrifluoromethane (Freon 13), dichloromonofluoromethane (Freon 21), monochlorodifluoromethane (Freon 22), trichlorotrifluoroethane (Freon 113), dichlorotetrafluoroehtane (Freon 114), monochloropentafluoroethane (Freon 115), 2,2-dichloro-1,1,1-trifluoroethane (Freon 123), 2-chloro-1,1,1,2-tetrafluoroethane (Freon 124), 1,2-dichloro-2,2-difluoroethane (Freon 132b), 1 chloro-2,2,2-trifluoroethane (Freon 133a), 1,1,1,2-tetrafluoroethane (Freon 134a), 1,1-dichloro-1,1,1-trifluoroethane (Freon 141b), 1-chloro-1,1-difluoroethane (Freon 142b), 1,1-difluoroethane (Freon 152a), 3-3-dichloro-1,1,1,2,2-pehtafluoropropane (Freon 225ca), 1,3-dichloro-1,1,2,2,3-pentafluoropropane (Freon 225cb) and octafluorocyclobutane (Freon C318). Moreover, AS-35 is also insoluble in mixtures of such propellants and commonly used solubilizing agents. Thus, it is impossible to prepare a solution type aerosol inhalation of AS-35.
The present invention is concerned with inhalations containing pyrido[1,2-a]pyrimidine compounds that are antiallergic drugs, and is directed to the provision of suspension type aerosol inhalations which are easy to carry and handle.
The requirements for suspension type aerosol inhalations are that the drug is suspended in the propellant and the dispersant, that the amount delivered is kept constant, that the drug particles are fine, and that they are physicochemically stable during long-term storage.
Delivery of the suspension in constant amounts means that the drug is applied to the affected part in constant doses. To this end, it is essential that the dispersibility of drug particles in the propellant be good. Accordingly, it is necessary to use dispersant which dissolves in the propellant and prevents the cohesion of drug particles. Moreover, the drug must not be soluble in the propellant or the dispersant because the crystals in drug particles may grow during long-term storage to cause clogging of the valve or variation in the amount delivered.
In order to allow a pyrido[1,2-a]pyrimidine compound to reach the affected part effectively, it is important that the pyrido[1,2-a]pyrimidine compound be in the form of fine particles. More specifically, it is preferable that the particles diameters be in the range of 0.01 to 10 .mu.m and at least 50% of the particles have a diameter of 2 to 5 .mu.m. Pyrido[1,2-a]pyrimidine compounds having such minute particle diameters can be obtained by pulverizing coarse particles thereof.
However, fine particles of pyrido[1,2-a]pyrimidine compounds (hereinafter referred to briefly as fine particles) tend to cohere. In order to prepare suspension type aerosol inhalations, such fine particles must be dispersed in a propellant.
For example, it has been reported that, when suspension type aerosol inhalations were prepared by using a pyrido[1,2-a]pyrimidine compounds selected from AS-35 and [9-(4-acetyl-3-hydroxy-2-n-propylphenoxymethyl)-4-oxo-pyrido[1,2-a]-pyrimi din-3-yl]-acetic acid (hereinafter referred to as AS-148), a propellant comprising a 4:6 mixture of Freon 11 and Freon 12, and a commonly used dispersant selected from propyleneglycol didecanoate (hereinafter referred to as PDD), diglyceryl mono-oleate (hereinafter referred to as DGMO-C), glyceryl dioleate (hereinafter referred to as DGO-80), tetraglyceryl hexacaprylate (hereinafter referred to as Sefsol 668), hexamethyltetracosane (hereinafter referred to as squalane), isopropyl myristate (hereinafter referred to as IPM) and polyoxyethylene (20) sorbitan mono-oleate (hereinafter referred to as Tween 80), the fine particles of AS-35 or AS-148 cohered to cause clogging of the valve or variation in the amount delivered. The present inventors have confirmed these findings by their own experiments. On the basis of their similarity in physicochemical properties, other pyrido[1,2-a]pyrimidine compounds are expected to behave in the same manner as AS-35 and AS-148.